I'm about to head to bed, but I want to try to answer your questions before I do. Here goes!
Having a cycle that is 36 days or less is considered totally normal. Having your cycle slowly get longer and longer isn't as normal if it isn't age related. (How old are you?) Having your LP start getting longer isn't normal either. Not to say that either signify a huge problem, but it's definitely not "normal", especially if you're under 36 years old.
Over 36 days is considered abnormal no matter what.
For any of these issues, it's worth having blood work done at CD3 to check to make sure your hormone levels aren't doing something weird. Getting a CD "21" blood draw at 7dpo to check estrogens and progesterone can also help doctors to get a better picture of your overall fertility levels. It needs to be done on 7dpo though, not actually on CD 21. A doctor who insists on CD 21 isn't worth what you're paying to being there.
CD 3 blood draw usually tests LH, FSH, all estrogens, and sometimes progesterone.
CD 21 tests progesterone and sometimes estrogens. (You want estrogens done, some doctors just don't check them on 7dpo for some reason.)
As far as temping goes, switching temping types is a no go. The vaginal temp and the under arm temp cannot be the same. It just doesn't work that way. Vaginal is by far more reliable, so if you're going to temp, that's generally the best way to go. If I were you, I'd start vaginally temping as soon as your period switches from flow to spotting. (Temps are erratic during flow anyway. They're only helpful for women who O very early in their cycles.)
You need to temp each of the 10 days prior to O to get the best visual reading by a person. It helps to establish pattern and people don't have a zillion charts in their head to pull from like FF does. If you ever need chart reading help, people will appreciate having the 10 days prior to looks at. It will also teach you how your cycles work so that you can predict what is happening a little better.
As far as FF goes- Skipping days near O will affect your reading. The 6 days prior to O are what your coverline is based on and they affect how the software analyses your chart.
Lastly, FF will leave a hollow dot for a few reasons. If you check "sleep deprived" on the "specifics" page you get a hollow circle, and same with temping more that about 29 minutes outside in either direction of your temp time average. I think there may be a couple other reasons, but I'll have to look them up tomorrow.